A few grammatical errors about learn-regex

[falaktheoptimist]

Fixed with #27

[priyadhoundiyal]

Not OP but can we reopen this? I found a few more grammatical errors.
"Imagine you are writing an application and you want to set the rules when user choosing their username. We want the username can contains letter, number, underscore and hyphen."
should be modified to:
"Imagine you are writing an application and you want to set the rules for when a user chooses their username. We want to allow the username to contain letters, numbers, underscore and hyphen."

In section 1, I think "A regular expression is just a pattern of letters and digits" should be replaced with:
"A regular expression is just a pattern of characters" since characters is generic and can be used to represent letters, digits and symbols.

In section 2,
"Some meta characters have a special meaning that are written inside the square brackets"
should be replaced with
"Some meta characters have a special meaning and are written inside square brackets"

In section 2.8
"In regular expressions, to check if the matching symbol is the starting symbol or ending symbol of the input string for this purpose we use anchors" should be replaced by
"In regular expressions, we use anchors to check if the matching symbol is the starting symbol or ending symbol of the input string"